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174
Br J Sports Med 2000;34:174–180
Suprascapular neuropathy in volleyball players
E Witvrouw, A Cools, R Lysens, D Cambier, G Vanderstraeten, J Victor, C Sneyers,
M Walravens
Department of
Rehabilitation
Sciences and
Physiotherapy, Faculty
of Medicine, Ghent
University, Belgium
E Witvrouw
A Cools
D Cambier
G Vanderstraeten
Faculty of Physical
Therapy and
Rehabilitation
Sciences, Catholic
University of Leuven,
Belgium
E Witvrouw
R Lysens
J Victor
C Sneyers
Ninnofse stwg 472, 1500
Halle, Belgium
M Walravens
Correspondence to:
Dr E Witvrouw, Department
of Rehabilitation Sciences
and Physiotherapy, Faculty
of Medicine, Ghent
University, De Pintelaan 185,
9000 Gent, Belgium
Accepted for publication
22 November 1999
Abstract
Background—Suprascapular nerve entrapment with isolated paralysis of the
infraspinatus muscle is uncommon. However, this pathology has been reported in
volleyball players. Despite a lack of scientific evidence, excessive strain on the
nerve is often cited as a possible cause of
this syndrome. Previous research has
shown a close association between shoulder range of motion and strain on the
suprascapular nerve. No clinical studies
have so far been designed to examine the
association between excessive shoulder
mobility and the presence of this pathology.
Aim—To study the possible association
between the range of motion of the shoulder joint and the presence of suprascapular neuropathy by clinically examining the
Belgian male volleyball team with respect
to several parameters.
Methods—An electromyographic investigation, a clinical shoulder examination,
shoulder range of motion measurements,
and an isokinetic concentric peak torque
shoulder
internal/external
rotation
strength test were performed in 16 professional players.
Results—The electrodiagnostic study
showed a severe suprascapular neuropathy in four players which aVected only
the infraspinatus muscle. In each of these
four players, suprascapular nerve entrapment was present on the dominant side.
Except for the hypotrophy of the infraspinatus muscle, no significant diVerences
between the aVected and non-aVected
players were observed on clinical examination. Significant diVerences between
the aVected and non-aVected players were
found for range of motion measurements
of external rotation, horizontal flexion and
forward flexion, and for flexion of the
shoulder girdle (protraction); all were
found to be higher in the aVected players
than the non-aVected players.
Conclusions—This study suggests an association between increased range of motion of the shoulder joint and the presence
of isolated paralysis of the infraspinatus
muscle in volleyball players. However, the
small number of patients in this study
prevents definite conclusions from being
drawn.
(Br J Sports Med 2000;34:174–180)
Keywords: suprascapular neuropathy; infraspinatus
muscle; volleyball; shoulder mobility
Shoulder problems have become common in
the overhead athlete. It is suggested that these
athletes are susceptible to injury and dysfunction because of the repetitious high velocity
mechanical stress placed on the shoulder, often
at extremes of glenohumeral motion.1 Nerve
lesions are a relative rarity among these athletes
compared with instability problems and rotator
cuV and acromioclavicular joint pathology.
Shoulder instability, specifically glenohumeral
instability, is defined as symptomatic translation of the humeral head on the glenoid during
motion.2 A review of the literature discloses
reports of suprascapular nerve palsy in
athletes.3–7 The most common lesion occurs at
the suprascapular notch, resulting in paralysis
of the common trunk of the nerve with
supraspinatus and infraspinatus hypotrophy.8
This entrapment was first described in 1963 by
Koppell and Thompson.9 No alternative entrapment site was recognised until 1981 when
the first case of spinoglenoid notch entrapment
was described by Ganzhorn et al.6 Entrapment
of the nerve at this site is considered very
unusual. However, isolated involvement of the
infraspinatus has been reported in volleyball
players and pitchers.5 7 10 Despite this knowledge, the pathogenesis of this entity is not yet
completely understood.
The suprascapular nerve is derived from the
upper trunk of the brachial plexus, receiving its
axons from the fifth and sixth cervical roots.
Mestdagh et al11 found, in their study on 20
human cadavers, almost no variation between
diVerent subjects in the origin of the suprascapular nerve. The nerve then courses laterally through the posterior triangle of the neck
across the scalenus medius muscle, under the
trapezius and omohyoideus to enter the
supraspinous fossa by obliquely passing
through the suprascapular notch. The nerve
continues its course laterally in the supraspinatus fossa, where it is in direct contact with the
belly of the supraspinatus muscle. On an average of 1 cm after passing the incisura, the nerve
provides motor fibres for the supraspinatus
muscle and a sensory fibre to the subacromial
bursa and glenohumeral and acromioclavicular
joints.
The nerve continues its course by curving
around the lateral border of the spine of the
scapula, the spinoglenoid notch, to gain
entrance to the infraspinatus fossa. This notch
is covered by the inferior transverse ligament or
spinoglenoid ligament, a narrow fibrous band
that forms a separation between the supraspinatus and infraspinatus muscle. The prevalence of this ligament has been reported to
range from 50 to 72%.12 13 The suprascapular
nerve then completes its course at a right angle
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175
Suprascapular neuropathy
and travels medially to the scapular spine. The
nerve is held against the bone by the belly and
musculotendinous part of the infraspinatus
and provides several successive branches to the
belly of the infraspinatus. Mestdagh et al11 have
shown that, in contrast with its origin,
individual variation in the terminal branches of
the suprascapular nerve is possible. Ferretti et
al5 postulated players whose suprascapular
nerve divides into three terminal branches
instead of into a plexus of motor branches may
be susceptible to the injury. When this variant
is present, the nerve forms an acute angle as it
curves around the lateral edge of the spine of
the scapula. It cannot be excluded that this
variation may partly explain why some volleyball players become injured and others do not.
There are no skin sensory endings for the nerve
as it is a motor nerve.
A review of the literature reveals several
hypotheses for the pathogenesis of isolated
paralysis of the infraspinatus muscle.
Trauma,14 15 strain,7 16 hypertrophy of the
spinoglenoid ligament,3 17 ganglion cysts,18 and
aberrant splitting of the terminal branches of
the nerve5 have all been reported as possible
causes of suprascapular nerve entrapment.
Although most reports appear to support the
theory of traction of the nerve as the cause of
suprascapular nerve entrapment, so far only a
few studies have investigated the correctness of
this hypothesis.19
Martin et al20 showed in their cadaver study
that the magnitude of suprascapular nerve
elongation was significantly dependent on
extreme arm positions. Their data indicate that
extreme motions in the shoulder girdle can
cause as much as 25% local elongation of the
suprascapular nerve. These data support
dynamic entrapment as a possible cause of
suprascapular neuropathy, and suggest that
players with large ranges of motion in the
shoulder girdle are prone to this injury.
However, this hypothetical association between
range of motion and the presence of suprascapular neuropathy has, to our knowledge,
never been investigated. Therefore it is the
purpose of this study to examine a possible
association between the range of motion of the
shoulder girdle and the presence of suprascapular neuropathy with isolated hypotrophy
of the infraspinatus muscle in volleyball
players.
Materials and methods
With the approval of the ethics committee of
the university hospital, we tested all the members of the Belgian male volleyball team (n =
16). Before participation, informed consent
was obtained from each subject. Of the 16
tested, 15 were right hand dominant. The subjects were aged from 20 to 35 years with a mean
age of 26. Their mean (SD) height was 195
(10.2) cm, and mean (SD) weight 89 (6.2) kg.
All were examined at the University Hospital
Pellenberg, Belgium.
ELECTROMYOGRAPHIC (EMG) EVALUATION
To quantify the muscles aVected by this
neuropathy, needle EMG measurements of all
shoulders (dominant and non-dominant) were
performed at four diVerent regions of the
supraspinatus and infraspinatus muscles.
Standard procedures consisting of standardised placement of surface electrodes to monitor
the responses on Erb’s point stimulation were
used to examine the conduction time.19 The
conduction time from the stimulating electrode
to the pick up needle was measured. The EMG
evaluation of all the players was performed by
the same qualified medical doctor, and the
results were not available to the other people
involved in the study.
CLINICAL EXAMINATION
A careful history was obtained by the same
orthopaedic surgeon for each athlete, to obtain
information on previous injuries and present
shoulder pain. A detailed physical examination
was also performed to acquire detailed information about the posture of the shoulder
girdle, possible hypotrophy, signs of impingement or instability, and to determine a possible
association between a neuropathy of the infraspinatus muscle and any of the above parameters.
With the athlete in the standing position, the
presence of any significant hypotrophy, any
deformities, and evidence of discoloration or
swelling were looked for in the anterior, posterior, and lateral view.
The physical examination proceeded with a
wall push up to evaluate serratus anterior
weakness. Abduction and forward flexion was
carried out to evaluate any asynchrony and
dyskinesia of the scapulothoracic rhythm or
glenohumeral movement. The physical examination included the impingement tests described by Hawkins and Kennedy21 and Neer.22
The instability assessment began with the
load and shift examination. As the head of the
humerus was loaded, both anterior and posterior stresses were applied, and the amount of
translation was noted in relation to the glenoid
rim. As prescribed by Hawkins and Bokor,23
the amount of translation was classified according to three types: type 1, normal translation or
head translates to the rim of the glenoid; type 2,
head translates over the rim; type 3, the head
locks out over the rim. For inferior instability,
the sulcus sign test was used. If the translation
occurs inferiorly, a visual sulcus sign appears
which is classified as inferior instability. The
next phase of stability assessment was to
attempt reproduction of instability symptoms
by the apprehension test.24 This test was
positive if apprehension of the patient to the
manoeuvre was provoked. It was carried out
with the subject in the supine position to obtain
maximum muscle relaxation. It is generally
accepted as a valid method of assessing shoulder instability.20 24
RANGE OF MOTION MEASUREMENTS
To obtain quantitative information about the
mobility of the shoulder girdle and a possible
left to right diVerence, the range of motion was
measured bilaterally, and assessed by standard
goniometric measurement.25 In addition, these
measurements can be used to investigate the
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176
Witvrouw, Cools, Lysens, et al
relation between shoulder mobility and the
presence of infraspinatus muscle neuropathy.
Active and passive external rotation was
assessed with the shoulder in 0°, 30°, and 90°
of abduction while the subject was in a supine
position. The active and passive internal
rotation was examined in the same supine
position with the shoulder in 90° of abduction.
The amount of forward flexion of the shoulder
was also assessed with the subject in this supine
position. To measure backward extension of
the shoulder, the subjects were placed in a
prone position on the examiner’s table. This
movement and the forward flexion were both
measured bilaterally in order to minimise compensation.
Horizontal flexion was measured with the
subject sitting on a stool to allow the scapula to
move freely along the thorax.
To measure the lateral displacement of the
scapula, the flexion and extension of the shoulder girdle (protraction and retraction) was
evaluated. The subject was sitting on a stool
and was asked to perform a maximal extension
of the shoulder girdle (retraction). In this position the horizontal distance (in cm) was
measured between the spinous process and the
angulus inferior of the medial border of the
scapula. Subsequently the subject was asked to
flex the shoulder girdle maximally (protraction), and the same measurement was repeated.
As many studies of joint measurements have
shown that intratester reliability is higher than
intertester reliability, in this study the same
examiner, who was experienced with these
measurements, performed all range of motion
evaluations. All measurements were performed
according to the guidelines of the AAOS.25
Riddle et al26 have shown that shoulder range of
motion measurements with a universal goniometer, as used in this study, is highly reliable.
They found, in their study on 50 patients,
intraclass correlation coeYcient values for
these measurements ranging from 0.94 to 0.98.
This was confirmed by others,27 28 and also by
our own reliability study of the lateral displacement measurement of the scapula, a measurement also used in this study.29 In this study,29
the intraclass correlation coeYcient for intratester reliability of this measurement ranged
between 0.96 and 0.8 (for 17 healthy subjects),
whereas for intertester reliability it was in the
range 0.42–0.9.
It can be questioned whether goniometric
measurements represent real joint or bony
motions. However, on the basis of the proven
validity of goniometric measurements in the
knee and hip joint,30–32 one can expect that
goniometric measurements of the shoulder
joint will also be valid.33
ISOKINETIC CONCENTRIC STRENGTH ASSESSMENT
To provide us with quantitative and accurate
data of muscle strength and left to right diVerences, bilateral isokinetic concentric peak
torque strength was measured by the same
qualified person, who was familiar with a
Cybex 350 isokinetic dynamometer. Concentric shoulder external/internal peak torque was
measured at 60°/s and 180°/s. Subjects were
positioned and secured by Velcro strapping
according to the Cybex testing manual (Cybex
I: Isolated joint testing and exercise;
Ronkonkoma, New York, 1983). With regard
to the reliability of testing, Kuhlmann et al34
showed high reliability of external rotational
isokinetic concentric peak torque measurements at 90°/s and 210°/s on 21 volunteers
with no history of shoulder pathology. This is in
agreement with the results of Greenfield et al,35
who found intratester correlation coeYcients
of 0.94 to 0.92 for external and internal
rotational isokinetic concentric peak torque
testing at 60°/s on 20 healthy volunteers.
STATISTICAL ANALYSIS
Means (SD) were calculated for the diVerent
characteristics. Given the small sample size and
the fact that the data are not normally distributed, Mann-Whitney U tests were performed
to compare the continuous variables between
the players who did and did not have
suprascapular neuropathy when there was a
normal distribution. A non-parametric Wilcoxon test was performed if the distribution did
not meet the criterion of normality. This was
the case for the active range of motion
measurements of (a) external rotation with the
arm in 0° of abduction on the dominant and
non-dominant side, (b) external rotation with
the arm in 30° of abduction on the dominant
side, (c) internal rotation with the arm in 0° of
abduction on the dominant and non-dominant
side, (d) flexion (protraction) on the dominant
and non-dominant side, (e) extension (retraction) on the dominant side.
A ÷2 or Fisher exact test was used to compare
the two groups for the discrete variables.
Significance was accepted at the 0.05 level.
Results
EMG MEASUREMENTS
The electrodiagnostic studies disclosed four
cases of isolated denervation in the infraspinatus muscle in the dominant shoulder. These
four players showed a complete motor drop out
of the infraspinatus muscle on full voluntary
eVort and at rest. We were unable to show any
electrical activity in this muscle in these
subjects. No abnormalities were found in the
supraspinatus muscle of these four players.
EMG nerve conduction velocities showed
complete denervation of the right (dominant)
infraspinatus muscle in the four subjects with
complete denervation of the infraspinatus
muscle. No abnormalities were found in the
supraspinatus muscle of these four players.
Table 1 displays anthropometric variables of
aVected and non-aVected players.
Table 1 Mean (X), standard deviations (SD) and
minimum and maximum values for height and weight of
aVected and non-aVected players
Height (cm)
Weight (kg)
AVected players
(n=4)
Non-aVected players
(n=12)
X
X
SD
min max
194 8.6 189 199
87 4.08 84 93
SD
min max
195 11.1 184 202
89 6.91 81 107
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177
Suprascapular neuropathy
min
max
p Value
10.1
13.8
74
69
100
102
0.66
0.02*
100
100
7.7
10
89
86
111
114
0.33
0.01*
145
147
115
118
6.9
10
105
104
123
130
0.001*
0.02*
7
6
19
13
19
10
2.5
2.8
14
6
24
15
0.65
0.41
15.9
10
162
177
198
201
171
173
21.5
7.9
146
164
194
184
0.67
0.02*
dominant side. There was no history of significant injury or pain in these four players, and
none complained of loss of function or even of
reduced eYciency when playing volleyball.
The Neer test was twice positive in the nondominant side of the non-aVected players and
once in the dominant arm of an aVected player.
The latter also showed instability of grade II in
the anterior direction and positive apprehension on the injured side. Of the non-aVected
players, one showed a slight positive load and
shift test anteriorly and a positive apprehension
test. In addition, two unaVected players
showed a load and shift test of grade I
anteriorly and posteriorly on the nondominant arm and one player on the dominant
arm.
16.6
6.4
194
199
230
217
196
194
9.1
11.1
185
180
204
207
0.13
0.04*
RANGE OF MOTION AND LAXITY
4.8
3.3
88
88
97
99
83
82
24.5
25.6
56
68
111
102
0.20
0.16
Table 2 Mean (X), standard deviations (SD) and minimum and maximum values for
the passive range of motion measurements of both groups
AVected players (n=4)
X
SD
External rotation in 0° Abd
Dom side
90
Non-dom side
104
External rotation in 30° Abd
Dom side
86
Non-dom side
115
External rotation in 90° Abd
Dom side
137
Non-dom side
134
Internal rotation
Dom side
11
Non-dom side
9
Horizontal flexion
Dom side
180
Non-dom side
186
Forward flexion
Dom side
211
Non-dom side
207
Backward extension
Dom side
93
Non-dom side
93
Non-aVected players (n=12)
min
max
X
10
6.0
77
96
104
112
87
85
5.6
5.9
80
105
92
122
6.3
10.2
128
121
5
2.1
SD
All values are presented in degrees, except internal rotation which is expressed in cm. Abd, abduction; dom, dominant.
*Significant at p<0.05.
Table 3 Mean (X), standard deviations (SD) and minimum and maximum values for
the active range of motion measurements of both groups
AVected players (n=4)
X
SD
External rotation in 0° Abd
Dom side
58
Non-dom side
75
External rotation in 30° Abd
Dom side
77
Non-dom side
90
External rotation in 90° Abd
Dom side
97
Non-dom side
108
Internal rotation
Dom side
11
Non-dom side
6
Horizontal flexion
Dom side
157
Non-dom side
163
Forward flexion
Dom side
199
Non-dom side
199
Backward extension
Dom side
45
Non-dom side
40
Non-aVected players (n=12)
min
max
X
7.2
6.6
50
68
67
85
69
64
8.2
10.4
70
78
88
102
6.6
10.6
90
95
5
2.3
SD
min
max
p Value
7.9
9.5
59
52
74
77
0.40
0.12
82
83
7.4
9
73
72
92
94
0.28
0.24
105
122
97
93
10.8
8.5
84
84
110
105
0.94
0.03*
5
4
18
9
12
10
4.1
3.6
6
7
17
15
0.60
0.54
4.1
7.6
150
153
164
173
153
158
18.1
9.3
133
147
174
169
0.81
0.36
15.7
10.6
185
187
220
209
183
182
10.2
11.9
172
168
191
193
0.03*
0.03*
6.6
10.3
38
31
55
54
41
42
17.6
21.1
22
23
55
57
0.69
0.88
All values are presented in degrees, except internal rotation which is expressed in cm. Abd, abduction; dom, dominant.
*Significant at p<0.05.
Table 4 Mean (X), standard deviations (SD) and minimum and maximum values for
the flexion and extension range of motion measurements of the shoulder girdle of both
groups
AVected players (n=4)
Flexion (protraction)
Dom side
Non-dom side
Extension (retraction)
Dom side
Non-dom side
Non-aVected players (n=12)
X
SD
min
max
X
SD
min
max
p Value
22
21
1.2
1.8
17
18
25
26
19
19
1.8
1.8
16
15
23
23
0.03*
0.04*
7
5
0.9
0.7
6
4
10
8
8
6
3.8
1
6
5
14
8
0.8
0.19
Table 2 gives mean (SD) values for passive
range of motion for both groups. Significant
diVerences between the two groups were found
on the dominant side for external rotation at
90° of shoulder abduction (p = 0.001). The
aVected players showed a significantly greater
range of motion for this movement than the
non-aVected players. For the non-dominant
side, a significant diVerence was found for
external rotation at 0°, 30°, and 90° of abduction (p = 0.02, p = 0.01, and p = 0.02 respectively), for horizontal flexion (p = 0.02), and for
forward flexion (p = 0.04) (table 2). As
observed for the dominant side, the aVected
players showed a greater range of motion than
the non-aVected players for these measurements.
Table 3 reports the results, after statistical
analysis, for the active movements. Significant
diVerences between the two groups were
observed on the non-dominant side for external rotation at 90° of shoulder abduction (p =
0.03) and for forward flexion (p = 0.03). For
each of these measurements, a significantly
greater range of motion was established for the
aVected players than the non-aVected players.
With regard to the active range of motion
measurements on the dominant side (table 3),
analysis of variance disclosed a significantly
greater forward flexion in the aVected players
than in the non-aVected players (p = 0.03).
With regard to mobility of the shoulder
girdle, the aVected players showed significantly
greater flexion (protraction) on both the dominant and non-dominant side (p = 0.03 and p =
0.04 respectively) than the unaVected players
(table 4). No significant diVerence was found
for the extension (retraction) of the shoulder
girdle between the two groups (p>0.05) (table
4).
FUNCTIONAL STRENGTH ASSESSMENT
All values are presented in cm. Dom, dominant.
*Significant at p<0.05.
CLINICAL INVESTIGATION
On physical examination, each athlete had
normal results for the wall push up, scapulothoracic rhythm, Kennedy test, and sulcus sign.
All four aVected players showed severe hypotrophy of the infraspinatus muscle on the
Table 5 shows the isokinetic concentric peak
torque characteristics of the internal and external rotation muscles of the dominant and nondominant shoulder of both groups. Significant
diVerences were identified between the affected and non-aVected players for internal
rotation isokinetic concentric peak torque
strength (p = 0.01). For this measurement, significantly higher values were obtained for the
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Witvrouw, Cools, Lysens, et al
Table 5 Mean peak torque (X), standard deviations (SD) and minimum and maximum
values for the isokinetic concentric peak torque data of both groups
AVected players (n=4)
X
Internal rotation 60°/s
Dom side
112
Non-dom side
107
Internal rotation 180°/s
Dom side
106
Non-dom side
94
External rotation 60°/s
Dom side
50
Non-dom side
66
External rotation 180°/s
Dom side
35
Non-dom side
48
Non-aVected players (n=12)
SD
min
max
X
SD
min
max
p Value
23.2
30.2
73
65
146
147
85
77
13.9
10.8
48
43
108
92
0.01*
0.01*
22.7
13.7
77
62
147
115
77
72
14.5
12.6
49
53
88
84
0.01*
0.01*
8.8
11.6
33
46
79
97
57
52
10.9
10.8
38
36
82
75
0.30
0.04*
7.5
5.1
24
36
47
62
42
37
9.1
10
26
31
55
47
0.21
0.07
All data are expressed in N.m/kg. Dom, dominant.
*Significant at p<0.05.
Table 6 Mean peak torque (X), standard deviations (SD) and minimum and maximum
values for the dominant and non-dominant isokinetic concentric peak torque data of the
aVected players (n=4)
Dominant side
Internal rotation
60°/s
180°/s
External rotation
60°/s
180°/s
Non-dominant side
X
SD
min
max
X
SD
min
max
p Value
112
106
23.2
22.7
73
77
146
147
107
94
30.2
13.7
65
62
147
115
0.32
0.15
50
35
8.8
7.5
33
24
79
47
66
48
11.6
5.1
46
36
97
62
0.03*
0.03*
All data are expressed in N.m/kg.
*Significant at p<0.05.
aVected players on both sides and for both test
velocities.
On examining the results of the external
rotation isokinetic concentric peak torque
strength (table 5), a significant diVerence was
found between the two groups when comparing the isokinetic concentric peak torque
strength at 60°/s on the non-dominant side (p
= 0.04). At this velocity, a significantly higher
value was observed in the aVected players.
A comparison of the isokinetic concentric
peak torque strength of the dominant with the
non-dominant side in the aVected players
showed a significantly decreased external rotation isokinetic concentric peak torque strength
on the injured side (p = 0.03) (table 6) at both
test velocities. No significant diVerence in
internal rotation isokinetic concentric peak
torque strength was observed between the two
shoulders in these players.
Discussion
The suprascapular notch, being a natural
foramen, is considered the most common site
of entrapment of the suprascapular nerve.5 7 16
With prolonged entrapment, hypotrophy of the
supraspinatus and infraspinatus muscle will
result. In most reports in the literature of
suprascapular nerve injury, both the supraspinatus and the infraspinatus muscle are
involved.36 37 Selective entrapment of the motor
branches of the infraspinatus muscle could
possibly occur if the nerve undergoes compression as it transverses and courses around the
edge of the lateral border of the spine of the
scapula. There are some reports of this pathology in the literature.3–5 12 38 Despite its rarity,
this pathology is sometimes observed in volley-
ball players.7 10 Its incidence (25%) in the Belgian male volleyball team in this study
compares favourably with values reported by
others.7 10 In our study, no abnormalities were
found in the supraspinatus muscle of the four
aVected players, suggesting that the spinoglenoid notch was probably the site of entrapment. However, because of the small number
of patients in this study, one must be very careful in translating these results into percentages.
In this study, none of the aVected players
complained of pain, loss of function, or even
reduced eYciency when they played volleyball.
This total absence of symptoms may on first
sight be very surprising, but is in accordance
with the findings of others.10 39 Because the
nerve has already provided a few sensory
filaments for the subacromial bursa before
reaching the point of entrapment, the site of
involvement could explain the total absence of
pain which has allowed the syndrome to go
undetected for so long, resulting in complete
irreversible denervation of the infraspinatus
muscle. Because paralysis of the infraspinatus
muscle results in loss of function of a major
humeral head depressor and creates a potential
imbalance in the force couple formed by the
deltoid and the rotator cuV muscles,40 we
expected to find more secondary shoulder
injuries in the aVected than the non-aVected
players. However, this was not the case. Our
observations confirm the results of Ferretti et
al,39 who found in their follow up study that
volleyball players who suVered from this
syndrome did not show progressive shoulder
dysfunction or any increased incidence of
painful overuse syndromes (impingement).
However, because of the small number of
patients in our study, we were unable to
compare the two groups statistically with
respect to instability and impingement signs.
Isokinetic concentric peak torque testing
disclosed a significant loss in external rotation
strength when the aVected shoulder was
compared with the unaVected side. This
finding is in agreement with the results of Ferretti et al5 and Ganzhorn et al,6 who both
observed an external rotation strength deficit in
the aVected shoulder.
We observed significantly higher bilateral
isokinetic concentric peak torque shoulder
strength in the aVected players than in the
non-aVected players for all strength measurements, except for the external rotation strength
of the injured side. On the basis of these data,
we conclude that the aVected players display
significantly greater overall isokinetic concentric peak torque shoulder strength than the
non-aVected players. Therefore the presence of
the suprascapular neuropathy is associated
with increased overall shoulder strength. However, these results must be interpreted with
great caution, as we only measured the strength
isokinetically and concentrically and used the
peak torque value, so we did not know the
players’ strength in various angles throughout
the range of motion, the eccentric strength, and
the force development at higher speeds or during the stretch shortening cycle. The last of
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179
Suprascapular neuropathy
these is extremely important to functional performance.
Although this selective hypotrophy of the
infraspinatus muscle, together with its symptoms, has been well described,5–7 38 the reason
why some players sustain this injury whereas
others, with similar amounts of training, do not
remains enigmatic. The present study was
designed to investigate the pathogenesis of this
nerve entrapment. Several mechanisms have
been proposed to explain the progressive, and
potentially irreversible, changes in the infraspinatus muscle. Most studies5 7 16 describe
traction, or stretching of the nerve, as the most
plausible pathomechanism. This traction injury may occur when repetitive overhead
activities result in local nerve strain that
exceeds the passive tolerance of the nerve.
Martin et al20 found that the magnitude of
elongation of the suprascapularis nerve was
significantly dependent on the rotation of the
scapula. Furthermore, they showed that extreme arm positions result in large rotations of
the scapula. They therefore concluded that
extreme shoulder positions may cause increased strain and subsequent ischaemia,
irritation, and swelling of the nerve. In
addition, Sandow and Ilic41 showed that
extreme shoulder abduction with full external
rotation places the suprascapular nerve in a
vulnerable situation. These extreme shoulder
movements are frequently and repetitively performed in all overhead sports activities. The
results of the studies of Martin et al20 and
Sandow and Ilic41 suggest that the greater the
shoulder mobility, the more vulnerable the
suprascapular nerve is to stretching.
In our study, the players with suprascapular
nerve entrapment displayed significantly
greater shoulder mobility than those without.
These diVerences in range of motion were
observed in the dominant and non-dominant
shoulder joint, and support the stretch theory
in the pathogenesis of this syndrome.
We acknowledge several potential limitations
of our study. One must bear in mind that the
small number of patients limits the interpretation of results. In addition, the mobility was
measured clinically. Despite several studies that
confirm the reliability of these measurements,
the standard errors suggest a need for cautious
interpretation of their precision. We recognise
that the error inherent in the measurements
make strict interpretation of the results unwarranted. In addition, no data are available on
their validity. Furthermore, we did not measure
directly the magnitude of the elongation of the
nerve. On the basis of other studies,20 we
assume that measuring shoulder mobility can
be regarded as an indirect assessment of the
amount of stretch of the nerve.
Looking at movements specific to volleyball,
the only two asymmetrical and powerful movements typical of the game are the service and
smash. In contrast with other authors,42 we
believe that the service and smash in volleyball
are not similar to the shoulder movement in
many other overhead sports. In volleyball, the
server does not aim for maximum speed, as in
pitching, but rather tries to send the ball in a
floating trajectory.43 To achieve this, the posterior muscles of the shoulder must provide a
braking action in the forward movement of the
serving arm. Therefore these muscles must be
eccentrically activated. This action increases
the distance between the points of origin and
termination of the nerve, and this may cause
tension of the nerve at the lateral edge of the
spinoglenoid notch.39 The fact that the incidence of this pathology in volleyball players is
high suggests that the nature of the game plays
an important role in the pathogenesis of this
lesion.
As the number of subjects that we examined
is limited, we must proceed with caution in
interpreting our results. The study can be considered as a pilot study for more extensive
investigations into the exact relation between
shoulder joint mobility and shoulder muscle
strength and the presence of suprascapular
neuropathy in volleyball players. Furthermore,
on the basis of the results of this study, we cannot exclude the possibility that other causes of
suprascapular entrapment suggested in the
literature—for example, ganglion cysts—may
be involved.
CONCLUSIONS
In this study the aVected players displayed a
bilateral greater shoulder isokinetic concentric
peak torque strength and shoulder mobility
than the unaVected players. This suggests that
congenitally greater shoulder mobility, possibly
combined with great overall isokinetic concentric peak torque shoulder strength, may place
volleyball players at greater risk of developing
this pathology. This may be explained by the
fact that greater shoulder mobility places the
suprascapular nerve in a more likely position to
be injured by traction.
It is tempting to ascribe the presence of this
pathology to the factors of mobility and
isokinetic concentric peak torque strength
which are shown in this study to be significantly associated with this injury. However, the
small sample size and the retrospective study
design limit the possibility of drawing definite
conclusions. Further research is required
before any conclusions about the relation
between this pathology and shoulder muscle
strength and mobility can be drawn.
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Take home message
Volleyball players with increased range of motion of the shoulder girdle appear to be more
likely to suVer suprascapular nerve entrapment with isolated paralysis of the infraspinatus
muscle.
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Suprascapular neuropathy in volleyball players
E Witvrouw, A Cools, R Lysens, D Cambier, G Vanderstraeten, J Victor, C
Sneyers and M Walravens
Br J Sports Med 2000 34: 174-180
doi: 10.1136/bjsm.34.3.174
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